Many beads are made from gemstone material. This section of All About Beads includes definitions of related terms, methods used for gemstone identification, and gemstone mining.
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What is a gemstone? Modern definitions vary. Some meanings of gemstones have strict guide lines: must have hardness of at least 7 on the Mohs scale; must be transparent, have luster, and high light refraction; must be mineral; must be rare enough to have a high monetary value; can include limited organic material.
All definitions of gemstones include 3 qualities:
2. Durable, hard enough to handle and wear
3. Rare enough to have value
What are gems? A gem has been defined as a mineral enhanced in some manner by altering its shape, usually by cutting and polishing. Sometimes the words gem and gemstone are used interchangeably.
The term precious gem, or precious gemstone, traditionally referred to diamonds, rubies, sapphires, and emeralds. Sometimes pearls were included. Semi-precious gemstone meant all other gemstones. The terms imply monetary value and have been used for marketing.
What are minerals? The definition of a mineral is a naturally occurring solid with a specific chemical composition and a distinctive internal chrystal structure. It is usually formed by inorganic processes. Most are chemical compounds. A few are single elements.
A crystal is a solid mineral with a geometric shape, straight edges, and smooth faces. Atoms are arranged in a regular, orderly way.
Another meaning of crystal refers to glass that contains lead.
An inclusion is a crystal or fragment of another substance enclosed in a crystal or rock. Inclusions in gemstones are important in determining the identity of a genuine gemstone. Their shapes in transparent colored gemstones can be seen using a microscope.
Matrix is fine grained rock which holds the gemstone crystal. Beads are often made from material that contains both the crystal and its matrix. Both matrix and inclusions can result in interesting combinations of colors and patterns.
Organic gemstones, such as pearls, coral, and amber, have their origin in plants and animals.
Synthetic gemstones, sometimes called lab created, are produced in laboratories and have physical and optical properties that are similar to the natural gemstone.They have the same chemical composition and crystal structure, but not the same inclusions.
Chemical elements which make up the composition of various gemstones
Gemology is the study of gemstones.
The unique physical properties of gemstones help to identify them.
Color is caused by the absorption or refraction of light.
Luster is the appearance of the surface in reflected light.
Streak is the color of the powder produced when the stone is scraped on a surface or crushed.
Cleavage is the ability to break into smooth flat surfaces.
Fracture describes other shapes of the edges when the mineral breaks.
Tenacity describes the ability to change shape without breaking.
Refractive index measures the velocity of light passing through a transparent or transluscent mineral. Fluorescence is the color of some minerals under ultraviolet light.
Symmetry is the geometric pattern of the crystals that make up the minerals. Symmetry is used to divide minerals into categories called crystal systems.
Habit is the complete description of the external shape of a crystal and includes all its visible characteristics.
Gemologists use many modern tests that give information about the properties, structure, and characteristics of gemstones. Most are important for identification. Two give information useful for choosing beads.
Mohs scale of hardness assigns numbers from 1 to 10, with 10 representing the hardest. The intervals between the values are not equal. The numbers for a gemstone can vary depending on the exact make up of a particular stone. The test uses scratching for the basis of hardness. A harder mineral will scratch a softer one, but not vice versa. Hardness is not an indication of toughness or strength. Hard minerals can be brittle.
Knowing the hardness of your beads can help you care for them.
A gemstone with a rating of:
1-2 can be scratched by a fingernail
3 can be scratched by a copper coin
4-5 can be scratched by a knife
6-8 can scratch glass
9-10 can cut glass
Diamond is the hardest gemstone and is not used for beads.
Specific Gravity measures density by comparing the weight of an object with an equal volume of water. The density of different kinds of gemstones is not the same. Using specific gravity, you can compare the weight of different varieties of gemstones of the same size. A higher number indicates a heavier stone. A strand of 8mm hematite (5.20) beads would be heavier than the same size strand of 8mm jasper (2.61) beads. Amber (1.08) is very light.
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It takes many centuries for gemstones to form deep under the earth’s surface. Through natural changes, they move upward. They can be found in a crystalline form embedded in host rock, in volcanic rock, cooled lava or ash, and as a result of erosion, on top of the ground.
There are two basic mining methods. Hard rock mining requires taking the gemstones from the rock in which they formed. In placer mining, the gemstones are separated from weathered rock debris where they have been released from the original rock.
A few mines use modern computer aided methods. Drilling and blasting are not used for most gemstones because they are shock sensitive. Earth moving bulldozers may be used in some mining operations. Many gemstone veins are in deteriorated rock and are mined by hand with pick and shovel.
Placer mining is used where gemstones have been released from rock by weathering. They may have been carried by water and can be found in river beds, beaches and the ocean floor. Mining methods use water to separate the gemstones from the gravel. The principle is the same as the old panning technique. The lighter materials are washed away. Gemstones are sorted out of the remaining gravel. In many countries this mining is also still done by hand.